Because the two tees are only a few pipe diameters apart, there is almost no pressure drop between them, so the secondary pump moves its circuit without pushing flow through the primary, and vice versa. That hydraulic separation lets boilers, zones and coils run at different flows and temperatures. Hydraulic separators and low-loss headers achieve the same effect in a single fitting.
Pipe the mod-con primary-secondary, its heat exchanger needs more flow than the system pump will give it.
Also heard as
- P/S
- primary/secondary
Related terms
Air separator
A hydronic fitting that pulls air bubbles out of circulating water and sends them out through an automatic vent.
Delta T
The temperature difference between supply and return water in a hydronic system.
Condensing boiler
A boiler designed to cool flue gas below its dew point so water vapor condenses and gives up its latent heat.
Pumping away
Placing a hydronic circulator just downstream of the expansion tank so it pushes water away from it.